Patulin is a mycotoxin produced by a variety of molds, in particular, Aspergillus and Penicillium and Byssochlamys. Most commonly found in rotting apples, in general the amount of patulin in apple products is viewed as a measure of the quality of the apples used in production. In addition, patulin has been found in other foods such as grains, fruits, and vegetables. While not considered a particularly potent toxin, a number of studies have shown patulin to be genotoxic, which has led some to theorize that it may be a carcinogen, although animal studies have remained inconclusive. Patulin has shown antimicrobial properties against some microorganisms. Several countries have instituted patulin restrictions in apple products. The World Health Organization recommends a maximum concentration of 50 µg/L in apple juice. In the European Union, the limit is set to 50 micrograms per kilogram (µg/kg) in both apple juice and cider, and to half of that concentration, 25 µg/kg, in solid apple products and 10 µg/kg in products for infants and young children. These limits came into force on 1 November 2003.